Treatment of synthetic fibers and apparatus therefor



Feb. 1, 1949.

/7 a /fi 6 l Q g /0 Z 81' u 1 '9: 4L 7 o Ma j I ma w 6' '20 l --wvw- &qyrtfilllllqyler (Ittorneg Imnentors Patented Feb. 1 19453 UNITED STATESPATENT OFFICE TREATMENT OF SYNTHETIC FIBERS AND APPARATUS THEREFORApplication November 19, 1943, Serial No. 510,870

11 Claims.

This invention relates to the treatment of fabric composed of syntheticfibres, and particularly to the problem of preventing such fabric fromcurling at the selvage edges.

Materials composed of synthetic fibres when woven, knitted or otherwisefabricated tend to curl at the edge. The formation of a selvage, bystarching or otherwise stiffening the edges of the material, isefiective in preventing such curling. The invention will be describedwith particular reference to the material known to industry as acetatetricot, though it is not, in any sense, limited to this material.Acetate tricot is ordinarily fabricated in sheets from to 12 feet wide.Curling may be prevented by stiffening a width of one-half inch at eachedge. The stiffening of the edges is also helpful in preventing'raveling or dissociation of a material because of its fibrous, openstructure.

Prior to this invention, it was proposed to stiffen the edges of suchmaterial by using starch or other chemicals. This treatment wasimpractical because the chemicals tended to run into the rest of thematerial. Heatin the edges by means of a hot iron was not satisfactorybecause if the iron was too hot or was applied for a longer period thanwas necessary, it was liable to stick to the material. In extreme cases,too hot an iron may melt or otherwise spoil the cloth.

It is an object, therefore, of our invention to provide an improvedmethod of and apparatus for stiffening materials continuously which isfree from the defects hereinbefore mentioned, and particularly animproved method and apparatus in which the heat to be used in thestifiening and the period for which it is applied may be adequatelycontrolled, and in which spoilage of material is prevented.

According to our invention, the material upon fabrication is fedcontinuously between a pair or pairs of electrodes which are connectedto a source of high frequency electrical energy. Because of itsdielectric losses the material is heated to the temperature required forstiffening, and means are adopted for preventing heat so developed fromunduly heating the electrodes. The application of slight pressurecompletes the stiffening process. This method and apparatus enable theoperator to maintain a degree of control far superior to any which wereobtainable by methods known to the prior art, and waste of material iscompletely eliminated.

The invention and its novel features will be best understood from thefollowing description of two embodiments thereof, when read in con- 2junction with the accompanying drawing, in which Figure 1 is a sectionalview in elevation of apparatus suitable for carrying out the invention;

Figure 2 is a plan view of the apparatus of Figure 1;

Figure 3 is a simplified diagram of a high frequency generator employedin the invention;

Figure 4 shows an alternative arrangement of electrodes;

Figure 5 is a side view of the biasing arrangement hereinaftermentioned;

Figure 6a is a plan view of a portion of one of the endless beltshereinafter mentioned, including a design to be impressed on a selvageedge, and

Figure 6b is a plan vie-w of a portion of selvage edge on which thedesign shown in Figure 6a has been impressed.

Referring to Figure 1, 2 represents the output end of a knitting orweaving machine (not shown) or other apparatus for the fabrication ofsheets of material composed of synthetic fibres. In the case of acetatetricot, the knitting or weaving speed is usually 8 inches per minute.The material 4 is preferably fed continuously as it emerges from themachine, between a pair of rotating circular electrodes 6-611. Theelectrodes may be biased mechanically by a spring l5 which urges theelectrodes toward each other whereby pressure is exerted upon thematerial between them. As shown in Figure 5, spring I5 is connected toshafts ll-l'la by a pair of sliding collars l9l9a within which theshafts rotate freely. The electrodes may be located near the point wherethe material leaves the knitting machine, or otherwise as close to thepoint of fabrication as may be convenient. Ordinarily there will be twopairs of electrodes, each pair adapted to receive one edge of theemerging sheet. In the embodiment shown, one of the electrodes 6 of apair is rotated by a motor 3 which is connected through a reduction gear5, a universal joint 1 and an insulated coupling 9. The other electrode6a of the pair is also connected through an insulated coupling, auniversal joint (which are not shown) and through a reversing gear IIwhich is connected to the motor 3 through the gear box 5. The electrodesrotate in opposite directions, together with heat insulating belts(hereinbefore described). The belts may act as a driving means forfeeding the material to be treated. However, if desired the electrodesmay be stationary or free wheeling and appropriate means (which may be apart of the knitting machine) may drive the fabric with respect to theelectric field.

As shown in Figure 1, each pair of electrodes has associated with it apair of endless belts 8-8a, made of cotton webbing or otherheatinsulating material. They are held on idler rollers I ll-llla. Theendless belts are interposed between each surface of the material 4 andthe electrodes 6-611. The belts heat insulate the electrodes so that theelectrode temperatures will not be unduly raised as the material isheated. If the belts were omitted, the electrodes, because of theircontact with the heated material, would gradually become heated. Whenthe temperature of the electrodes is raised, the material becomes tackyand sticks to the electrodes in the absence of the belts. In order thatthe power, which is applied through the belts, should not heat thebelts, they are preferably made of a material having very low dielectriclosses. In any event the belts, being in contact with the heatedmaterial, will be heated by such contact. The belts will quickly radiatesuch heat, if they are made relatively long and are exposed so that theheat is not confined.

If short belts are required because ofspace limitations, their radiationmay be increased by directing an air stream or other coolant on thebelts. It should be understood that belts may include any desiredpattern which may be impressed upon the selvage edge. Figure 6a shows aportion of a belt bearing a design in intaglio, and Figure 6b a portionof selvage edge on which that design has been impressed in cameo.

Electrodes 6-6a are connected to an oscillator or other source of highfrequency electrical energy. Figure 2 is a diagram of such anoscillator. Frequencies of from 200 to 300 megacycles per second havebeen found practical for this application, though the operation is notlimited to those frequencies. However, if such frequencies are employed,it is possible to keep the voltage applied to the electrode withinconvenient limits, so that the possibility of voltage breakdown iseliminated. Two 826 tubes are connected in a push-pull arrangement, andthe electrodes are coupled to the filament circuit. The grid andfilament circuits may be tuned by connecting bars or links l2, I4.

High frequency electric energy from the oscillator establishes anelectric field between the electrodes. The material passing between theelectrodes, because of the dielectric losses of the material, becomesuniformly and quickly heated. The application of slight pressure asbefore described in addition to the heat causes the edge of the materialto become stiff, and in this way, prevents the material from curling.

While the edge of the material to be stiffened should pass through thefield set up between the electrodes, it may often be convenient to haveboth electrodes engage one surface only of the material. Figure 4 showssuch an arrangement. The electrodes 66a engage only one surface of thematerial 4, which may be supported, as by the table top 16. In thisarrangement only one endless member 8 need be employed. The materialcuts lines of force (shown by dotted lines) set up between theelectrodes, and heat is developed therein as before described.

We have described an improved process and apparatus for preventingsheets of material composed of synthetic fibre from curling, by passingthe edges of the sheet, continuously upon fabrication, through a highfrequency electric field,

and thereby developing heat within such edges, which with the aid ofslight pressure, stiifens them. Our invention is not, however, limitedto this specific application. Any portion of the material, or all of it,may be stiffened by passing it through a field as aforesaid; andmaterial not composed of synthetic fibre may be stiffened by theincorporation therein of fibre having sufficiently high dielectriclosses and appropriate stiffness characteristics upon being heated.

We claim as our invention:

1. Apparatus for stiffening a portion of a fabric sheet woven fromsynthetic fibers which become tacky when raised to a certaintemperature, said apparatus comprising a pair of unheated electrodes, asource of high frequency electricity, means connecting said electrodesto said source for the production of an electrostatic fieldthereadjacent and therebetween, a belt consisting of heat and electricalinsulating material contacting a surface of said electrodes, meansincluding said electrodes and said belt for passing a portion of saidfabric sheet through said electric field, in contact with a surface ofsaid belt but out of contact with said electrodes, and means includingsaid electrodes for exerting a predetermined pressure on a portion ofsaid fabric sheet being subjected to said electric field.

2. Apparatus according to claim 1 characterized by the addition thereto,and in combination therewith, of means for absorbing heat developed insaid belt.

3. Apparatus according to claim 1 characterized by the addition of meansassociated with said belt for simultaneously impressing a pattern on aportion of said fabric being subjected to said electric field.

4. Apparatus for stiffening a portion of a fabric sheet woven fromsynthetic fibers which become tacky when raised to a certaintemperature, said apparatus comprising a pair of unheated electrodespositioned side by side and adapted to be pressed against only one sideof said fabric sheet, a source of high frequency electricity, meansconnecting said electrodes to said source for the production of anelectrostatic field thereadjacent and therebetween, a belt consisting-ofheat and electrical insulating material contacting a surface of saidelectrodes, means for passing a portion of said fabric sheet throughsaid electric field in contact with a surface of said belt but out ofcontact with said electrodes, and means including said electrodes forexerting a predetermined pressure on a portion of said fabric sheetbeing subjected to said electric field.

5. Apparatus of claim 1 in which said electrodes are narrow rollers andsaid fabric feeding means is adapted to pass only a narrow edge portionof said fabric sheet through said electric field.

6. A method of forming a stiffened selvage on sheets of woven fabricmaterial made of synthetic fibers which become tacky when raised to acertain temperature, said method comprising subjecting an edge portionof said sheets to the heating effect of a high frequency electric fieldof a frequency and intensity sufiicient to raise said portion to atemperature just below the point at which it becomes tacky, and applyingpredetermined pressure to said heated portion whereby to stiffen it andprevent edge-curling.

7. A method of stiffening a portion of a fabric sheet woven fromsynthetic fibers which become tacky when raised to a certaintemperature, said method comprising establishing between a pair ofelectrodes a high frequency electric field of an intensity and frequencysuflicient to raise said portion to a temperature just below the pointat which it becomes tacky, moving said portion ofapplying predeterminedpressure to said portion while it is being heated, in order to stiffenit.

8. The method of claim 6 in which said portion is an edge portion.

9. The method of forming a stiffened selvage with an embossed pattern onsheets of fabric woven from synthetic fibers which become tacky whenraised to a certain temperature, said method including forming astiffened selvage on said sheets by subjecting an edge portion of saidsheets to the heating effect of a high frequency electric field of afrequency and intensity sufficient to raise said portion to just belowthe point of tackiness, and applying embossing pressure to said portionwhile in said heated state.

10. Apparatus for stiffening a portion of a sheet material composed offibers which become tacky when raised to a certain temperature, saidapparatus comprising unheated rollers having sheet contacting surfacesfor exerting pressure upon the sheet, resilient means for urging saidrollers in a direction normal to the direction of travel of a sheetthrough the apparatus, means forming a high frequency electric source,means connecting said rollers as electrodes to said source for theproduction of an electric field therebetween and thereadjacent, a beltconsisting of heat and electrical insulating material for thermally andelectrically insulating said sheet from said rollers, and meansincluding at least one of said rollers and said belt for advancingsheets to be treated through said electric field and in contact withsaid belt.

11. In a method of forming a stiffened selvage on woven fabric materialcomposed of fibers which become tacky when raised to a certaintemperature, said method comprising generating sufficient heat within anedge portion of the material so that its temperature is raised to apoint just below the point at which the fibers become tacky, andsubjecting the heated portion of the fabric to predetermined stiffeningpressure by unheated rollers which also serve as electrodes betweenwhich high frequency electric field is established for generating saidheat within the fabric, the improvement which consists in thermallyinsulating the fabric from the rollers whereby said rollers areprevented from becoming heated and the fabric is prevented from beingheated to the point of tackiness.

GEORGE H. BROWN. CYRIL N. HOYLER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 211,009 Hagerty Dec. 1'7, 1878869,895 Goldman Nov. 5, 1907 1,803,672 Lardy May 5, 1931 1,954,635Leonard, Jr Apr. 10, 1934 2,319,174 Wilson May 11, 1943 2,324,068Crandell July 13, 1943 2,423,902 Peterson July 15, 1947

